Hydrocarbon conversion

ABSTRACT

This invention relates to the conversion of substantially-saturated hydrocarbon to higher-value hydrocarbon products such as aromatics and/or oligomers, to equipment and materials useful in such conversion, and to the use of such conversion for, e.g., natural gas upgrading.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/543,243, filed Nov. 17, 2014, which claims priority to ProvisionalU.S. Patent Application Ser. No. 61/912,877, filed Dec. 6, 2013, thedisclosures of which are incorporated herein by reference in theirentireties. This application also claims priority to European PatentApplication No. EP 14153941.1, filed Feb. 5, 2014, the disclosure ofwhich is incorporated herein by reference in its entirety. Crossreference is made to the following related patent applications: (i)P.C.T. Patent Application No. PCT/US2014/065947, filed Nov. 17, 2014;(ii) U.S. patent application Ser. No. 14/543,271, filed Nov. 17, 2014;(iii) P.C.T. Patent Application No. PCT/US2014/065956, filed Nov. 17,2014; (iv) U.S. patent application Ser. No. 14/543,365, filed Nov. 17,2014; (v) P.C.T. Patent Application No. PCT/US2014/065969, filed Nov.17, 2014; (vi) U.S. patent application Ser. No. 14/543,426, filed Nov.17, 2014; (vii) P.C.T. Patent Application No. PCT/US2014/065961, filedNov. 17, 2014; and (viii) U.S. patent application Ser. No. 14/543,405,filed Nov. 17, 2014.

FIELD

This disclosure relates to the conversion of substantially-saturatedhydrocarbon to higher-value hydrocarbon products such as aromatics, toequipment and materials useful in such conversion, and to the use ofsuch conversion for, e.g., natural gas upgrading.

BACKGROUND

Although methane is abundant, its relative inertness has limited itsutility in conversion processes for producing higher-value hydrocarbons.For example, oxidative coupling methods generally involve highlyexothermic and potentially hazardous methane combustion reactions,frequently require expensive oxygen generation facilities and producelarge quantities of environmentally sensitive carbon oxides. Inaddition, non-oxidative methane aromatization is equilibrium-limited,and temperatures ≧ about 800° C. are needed for methane conversionsgreater than a few percent.

To obviate this problem, catalytic processes have been proposed forco-converting methane and one or more co-reactants to higherhydrocarbons, such as aromatics. For example, U.S. Pat. No. 5,936,135discloses reacting methane at a temperature in the range of 300° C. to600° C. with (i) a C₂₋₁₀ olefin and/or (ii) a C₂₋₁₀ paraffin in thepresence of a bifunctional pentasil zeolite catalyst, having strongdehydrogenation and acid sites, to produce aromatics. The preferred moleratio of olefin and/or higher paraffin to methane and/or ethane in thefeed ranges from about 0.2 to about 2.0.

Other processes utilize organic oxygenate as a co-reactant for thenon-oxidative methane conversion to produce higher hydrocarbons,including aromatics. For example, U.S. Pat. No. 7,022,888 discloses aprocess for the non-oxidative conversion of methane simultaneously withthe conversion of an organic oxygenate, represented by a generalformula: C_(n)H_(2n+1)OC_(m)H_(2m+1), wherein C, H and O are carbon,hydrogen and oxygen, respectively; n is an integer having a valuebetween 1 and 4; and m is an integer having a value between zero and 4,to C₂₊ hydrocarbons, particularly to gasoline range C₆-C₁₀ hydrocarbonsand hydrogen, using a bifunctional pentasil zeolite catalyst, havingstrong acid and dehydrogenation functions, at a temperature below 700°C.

There is, however, interest in developing alternative routes for theconversion of methane into aromatics and particularly routes that allowmore methane to be incorporated into the aromatic product and thatallows a broader molar ratio range of methane to co-reactant in thefeed.

SUMMARY

It has now been found that using acetylene as the co-reactant allowssubstantially-saturated hydrocarbon, such as one or more of methane,ethane, propanes, butanes, pentanes, etc., to be converted to aromaticsand/or oligomers. The aromatics products are generally rich in tolueneand xylenes. The conversion can generally be carried out at relativelylow temperature compared to conventional processes, and with a lesseramount of co-reactant per unit weight of aromatics produced. In someaspects, the substantially-saturated hydrocarbon comprises methane.Optionally, the methane is obtained from natural gas, e.g., wet naturalgas. Besides methane, wet natural gas contains a significant amount of asecond substantially-saturated hydrocarbon, e.g., C₂ to C₅ alkane. It isobserved that the presence of the second substantially-saturatedhydrocarbon in the feed improves methane conversion and yields higherselectivity to liquid products (such as aromatics) at lower reactiontemperatures.

Accordingly, one aspect of the present disclosure resides in a processfor producing aromatics. The process comprises a first step whichincludes providing a feed comprising acetylene and at least 9 mole % ofa first substantially-saturated hydrocarbon, based on per mole of feed,wherein the molar ratio of substantially-saturated hydrocarbon toacetylene in the feed is in the range of from 0.6:1 to 20:1. The processcontinues with a second step, which includes contacting the feed with acatalyst comprising at least one molecular sieve component and at leastone dehydrogenation component under conditions, including a temperatureof at least 300° C., effective to convert at least part of the acetyleneand the first substantially-saturated hydrocarbon in the feed to aproduct comprising at least 5 wt. % of C₅₊ hydrocarbon, such asaromatics, based on the weight of the product. At least a portion of thearomatics can be separated from the product and conducted away from theprocess, e.g., for storage and/or further processing. Optionally, thefirst substantially-saturated hydrocarbon comprises ≧90.0 wt. % ofmethane, based on the weight of the first substantially saturatedhydrocarbon. The feed can further comprise at least 9 mole % of a secondsubstantially-saturated hydrocarbon, based on per mole of feed. Thesecond substantially-saturated hydrocarbon can comprise, e.g., ≧90.0 wt.% of alkane, such as one or more C₂ to C₅ alkane, based on the weight ofthe second substantially-saturated hydrocarbon. At least part of themethane and C₂ to C₅ alkane in the feed are optionally derived fromnatural gas, e.g., from wet natural gas.

In a further aspect, the present disclosure resides in a process forproducing aromatics which includes providing a feed comprisingacetylene, at least 9 mole % of methane, and at least 9 mole % of one ormore C₂ to C₅ alkane, the mole percents being based on per mole of feed,wherein the molar ratio of methane to acetylene in the feed is in therange of from 0.6:1 to 20:1. The process includes contacting the feedwith a catalyst comprising at least one molecular sieve and at least onedehydrogenation component under conditions, including a temperature ofat least 300° C., effective to convert at least part of the methane, C₂to C₅ alkane, and acetylene in the feed to a product comprising at least5 wt. % of aromatics, based on the weight of the product. At least partof the aromatics can be separated from the product, e.g., for storageand/or further processing. The molecular sieve can comprise, e.g., oneor more aluminosilicate and/or a substituted aluminosilicate having aConstraint Index from 2 to 12, such as ZSM-5 or ZSM-11. Thedehydrogenation component can comprise, e.g., at least one metal orcompound thereof from Groups 3 to 13 of the Periodic Table, such as ametal or compound thereof selected from Ga, Zn, Cu, Re, Mo, W, La, Fe,Ag, Pt, Pd, and mixtures thereof.

In yet another aspect, the present disclosure resides in a process forproducing C₅₊ hydrocarbon. The process includes a first step ofcontacting a feed comprising methane with an oxygen-containing gas inthe presence of a first catalyst under conditions effective tooxidatively couple the methane to produce an effluent containing C₂₊hydrocarbon and unreacted methane. In a second step, acetylene and atleast a portion of the first step's unconverted methane react in thepresence of a second catalyst, the second catalyst comprising at leastone molecular sieve and at least one dehydrogenation component. Thesecond step's reaction is carried out under conditions effective forconverting the acetylene and at least part of the first step's unreactedmethane to a product comprising C₅₊ hydrocarbon. Reaction conditions inthe second step can include exposing the unreacted methane to atemperature of at least 500° C. Optionally, the entire effluent of thefirst step is reacted with the acetylene in the second step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show the Gibbs free energy of formation per carbon atomfor exemplary carbon-containing compounds as a function of eachcompound's hydrogen:carbon H/C atomic ratio at 600° C. (FIGS. 1) and400° C. (FIG. 2), at 1 atmosphere pressure. Aromatics are represented bydiamond points. The line through the diamond points representspolynuclear aromatic compounds. The open diamond point representsacetylene. The solid circle point represents graphite. The solid circlewith a protruding line (upward protruding line in FIG. 1, downwardprotruding line in FIG. 2) represents C₂ olefin (the circle) and C₃ toC₈ olefin (the protruding line). Cyclohexane is represented by an “x”.C₁₊ normal paraffin is represented by solid rectangles.

DETAILED DESCRIPTION

Definitions

For the purpose of this specification and appended claims, the followingterms are defined. The term “Cn” hydrocarbon wherein n is a positiveinteger, e.g., 1, 2, 3, 4, or 5, means a hydrocarbon having n number ofcarbon atom(s) per molecule. The term “Cn+” hydrocarbon wherein n is apositive integer, e.g., 1, 2, 3, 4, or 5, means hydrocarbon having atleast n number of carbon atom(s) per molecule. The term “Cn−”hydrocarbon wherein n is a positive integer, e.g., 1, 2, 3, 4, or 5,means hydrocarbon having no more than n number of carbon atom(s) permolecule. The term “aromatics” means hydrocarbon molecules containing atleast one aromatic core. The term “substantially-saturated hydrocarbon”means hydrocarbon comprising ≦1.0 mole % of molecules which contain atleast one double and/or at least one triple bond. The term “hydrocarbon”encompasses mixtures of hydrocarbon, including those having differentvalues of n. As used herein, the numbering scheme for the groups of thePeriodic Table of the Elements is as disclosed in Chemical andEngineering News, 63(5), 27 (1985).

The present disclosure relates to producing aromatics by reacting a feedcontaining acetylene; a first substantially-saturated hydrocarbon, suchas methane; and, optionally, a second substantially-saturatedhydrocarbon, e.g., C₂ to C₅ alkane. The feed is reacted in the presenceof a catalyst, e.g., a bifunctional catalyst comprising (i) at least onemolecular sieve component and (ii) at least one dehydrogenationcomponent. Although the mechanisms of the reactions occurring in thepresent process are not fully understood, it is believed thatsubstantially-saturated hydrocarbon, such as methane, is activated bythe acetylene at the metal and acid sites of the bifunctional catalystallowing the substantially-saturated hydrocarbon to be aromatized attemperatures ≦700° C., e.g., ≦500° C. In addition, it is found that when(i) the first substantially-saturated hydrocarbon comprises methane and(ii) the feed further comprises a second substantially-saturatedhydrocarbon such as C₂ to C₅ alkane, methane aromatization occurs ateven lower temperatures, e.g., ≦475° C.

The advantages achieved by present process are illustrated in Table 1which lists the Gibbs free energy of formation ΔG_(Rxn) for theformation of 1 mole of benzene from several different hydrocarbonmixtures. The calculations are carried out using data disclosed in: (i)Stull et al., The Chemical Thermodynamics of Organic Compounds, 1987;(ii) Yaws, C. L., Chemical Properties Handbook, McGraw Hill, 1999.

TABLE 1 Moles of H₂ generated ΔG_(Rxn) per mole of (kcal/mole benzene)Rxn # Reaction benzene 300° C. 500° C. 650° C. 800° C. 1 6CH₄ → C₆H₆ +9H₂ 9 75.4 49.4 28.1 5.4 2 4CH₄ + 2/3C₃H₈ → C₆H₆ + 7.7 54.2 28.2 6.9−15.8 23/3H₂ 3 4CH₄ + C₂H₂ → C₆H₆ + 6H₂ 6 18.2 6.6 −3.4 −14.1 4 CH₄ +C₃H₈ + C₂H₂ → C₆H₆ + 4H₂ 4 −13.6 −25.3 −35.2 −45.9 5 4/3C₃H₈ + C₂H₂ →C₆H₆ + 3.3 −24.1 −35.9 −45.8 −56.5 10/3H₂ 6 2CH₄ + 2C₂H₂ → C₆H₆ + 3H₂ 3−39.0 −36.3 −34.8 −33.7 7 3C₂H₂ → C₆H₆ 0 −96.2 −79.2 −66.3 −53.2

Table 1 summarizes the ΔG_(Rxn) for the formation of 1 mole of benzene,optionally in the presence of one or more of the specified catalyst,from feeds comprising one or more of methane, propane and acetylene. Thetable shows reaction conditions are more favorable when fewer moles ofH₂ are generated per mole of benzene, e.g., a specified conversion canbe achieved at a lower temperature. In particular, it is observed thatacetylene is a more efficient co-reactant than are olefins, and olefinsare more efficient co-reactants than are paraffins. For example, thearomatization of pure methane (Rxn No. 1) proceeds at temperatures above750° C. By contrast, the co-conversion of methane and acetylene tobenzene can occur at a much lower temperature, e.g., in the range offrom 300° C. to 650° C. (Rxn Nos. 3 and 6). As the relative amount ofacetylene in the feed is increased (exemplified by Rxn No. 6), itbecomes increasingly desirable to operate the reaction at a relativelylow temperature, e.g., in the range of 300° C. to 600° C., such as inthe range of 300° C. to 500° C. It is believed that the desirability oflow to moderate reaction temperatures at a methane:acetylene molar ratio≦2.0, e.g., ≦1.0, such as ≦0.5, results from kinetic effects, such as anincrease in acetylene-acetylene reactions that are kinetically favoredover methane aromatization at temperatures ≧600° C., e.g., ≧650° C.,such as ≧700° C., or ≧800° C. The table shows that although thecatalytic co-conversion of methane and propane (Rxn No. 2) is morefavorable than conversion of methane (Rxn No. 1) and can be carried outabove 650° C. (ΔG_(Rxn), =−0.54 kcal/mole at 700° C.), it is not asthermodynamically favorable as reactions which include acetylene as aco-reactant (see, e.g., Rxn Nos. 3-7). It is observed that otherco-reactants, such as one or more paraffins and olefins, react in a waysimilar to that of Rxn No. 2. Rxn No. 4 and No. 5 show that thefavorable thermodynamics arising from the use of an acetyleneco-reactant are also attained when a C₂₊ alkane is substituted for atleast a portion of the methane as primary reactant. In other words,using acetylene as a co-reactant with methane, methane-paraffin,methane-olefin and methane-paraffin-olefin (e.g. natural gas) mixturesresults in more facile reactions, lowering the temperature requirementsinto the range of from 300° C. to 500° C., e.g., 300° C. to 400° C.,such as 300° C. to 350° C., as illustrated by Rxn Nos. 3, 4, 5, and 6.

Similarly, FIGS. 1 and 2 qualitatively illustrate the favorableenergetics resulting from the use of acetylene as a co-reactant inalkane aromatization. As shown in the figures, blending acetylene withmethane (and other light alkane), lessens the average Gibbs free energyof formation. For example, FIG. 1 shows that at 600° C., approximately10 kcal/mol of carbon is needed for converting methane to benzene. Asthe figure shows, the favorable energy difference can be provided by anacetylene co-reactant, ≧about 10 kcal/mole of carbon compared tobenzene. Energetically, therefore, utilizing acetylene as a co-reactantis far more favorable than using C₂ to C₈ olefin (a boost of <about 5kcal/mole carbon) or C²³⁻ paraffin (a boost of <about 6 kcal/mole ofcarbon). FIG. 2 shows that at 400° C., approximately 12 kcal/mole ofcarbon is needed for converting methane to benzene. As the figure shows,the favorable energy difference can be provided by acetyleneco-reactant, ≧15 kcal/mole of carbon compared to benzene. Energetically,therefore, utilizing acetylene as a co-reactant is far more favorablethan using C₂ to C₈ olefin (a boost of <4 kcal/mole carbon) or C²³⁻paraffin (a boost of <3 kcal/mole of carbon). In other words, thefigures show that the presence of the acetylene co-reactant more thancompensates for the energy change that would otherwise be needed whenaromatizing methane. Certain feeds useful in aspects of the inventionwill now be described in more detail. The invention is not limited tothese feeds, and this description is not meant to foreclose the use ofother feeds within the broader scope of the invention.

In certain aspects, the feed is primarily in the vapor phase duringaromatization, e.g., ≧90.0 wt. % of the feed is in the vapor phase,based on the weight of the feed, such as ≧99.0 wt. %. The feed cancomprise acetylene and at least 9 vol. % of a firstsubstantially-saturated hydrocarbon, based on the volume of feed. Thefirst substantially-saturated hydrocarbon can comprise e.g., ≧50.0 wt. %of methane, based on the weight of the first substantially-saturatedhydrocarbon, such as ≧75.0 wt. %, or ≧70.0 wt. %, or ≧99.0 wt. %. Themolar ratio of first substantially-saturated hydrocarbon to acetylene inthe feed can generally be in the range of from 0.6:1 to 20:1, such asfrom 5:1 to 15:1, for example from 7:1 to 10:1. For example, the molarratio of methane to acetylene in the feed can be in the range of from0.6:1 to 20:1, such as from 5:1 to 15:1, for example from 7:1 to 10:1.

Optionally, the feed comprises ≧9 mole % of methane and furthercomprises ≧0.1 mole %, e.g., ≧9 mole %, of a secondsubstantially-saturated hydrocarbon, the mole percents being based onper mole of feed, wherein the molar ratio of methane to acetylene in thefeed being in the range of from 0.6:1 to 20:1. The secondsubstantially-saturated hydrocarbon can comprise, e.g., ≧50.0 wt. % ofone or more C₂ to C₅ alkane, based on the weight of the secondsubstantially-saturated hydrocarbon, such as ≧75.0 wt. %, or ≧90.0 wt.%, or ≧99.0 wt. %. Optionally, the feed further comprises ≧0.1 mole %diluent, based on per mole of feed. Diluent generally comprises specieswhich do not react in significant amounts with substantially-saturatedhydrocarbon to produce aromatics under the specified operatingconditions. Suitable diluent includes one or more of molecular hydrogen;carbon oxides, such as carbon monoxide, carbon dioxide, and includingcarbon oxides of non-integral stoichiometry, hydrogen sulfide, andmolecular nitrogen. In certain aspects, the feed comprises diluent in anamount in the range of from 0.1 mole % to 50 mole %, based on per moleof feed. Where present, some or all of the diluent can be present asby-products of the process used to produce the feed's acetylene and/orsubstantially-saturated hydrocarbon.

In certain aspects, the first substantially-saturated hydrocarboncomprises ≧99.0 wt. % of methane, based on the weight of the firstsubstantially-saturated hydrocarbon, and the sole co-reactant in thefeed is acetylene. For example, besides acetylene, methane, and diluent,the feed can comprise ≦1.0 mole % of other constituents, based on permole of feed, e.g., ≦0.1 mole %, such as ≦0.1 mole %. In these aspects,for example, the molar ratio of methane to acetylene in the feed canrange from 0.6:1 to 20:1, such as from 5:1 to 15:1, for example from 7:1to 10:1. Examples of suitable feeds comprise from 80 mole % to 99 mole %of methane and from 1 mole % to 20 mole % acetylene, based on per moleof feed, such as from 85 mole % to 99 vol. % of methane and from 1 mole% to 15 mole % acetylene. The remainder of the feed, if any, cancomprise diluent, for example.

In certain aspects, first substantially-saturated hydrocarbon comprises≧99.0 wt. % of methane, based on the weight of the firstsubstantially-saturated hydrocarbon, and the feed further comprises ≧0.1mole % of a second substantially-saturated hydrocarbon, based on permole of feed, e.g., ≧1.0 mole. %, such as ≧10.0 mole %. When, forexample, the second substantially-saturated hydrocarbon comprises ≧50.0wt. % of C₂ to Cs alkane, based on the weight of the secondsubstantially-saturated hydrocarbon, e.g., ≧90.0 wt. %, such as ≧99.0wt. %, then (i) the molar ratio of methane to acetylene in the feed canbe in the range of from 0.6:1 to 20:1, such as from 4:1 to 10:1, forexample from 5:1 to 10:1; and (ii) the molar ratio of C2 to C5 alkane toacetylene in the feed can be in the range of from 0.1:1 to 20:1 such asfrom 2:1 to 10:1, for example from 3:1 to 10:1. Examples of suitablefeeds comprise from 40 mole % to 80 mole % of methane, from 1 mole % to15 mole % acetylene and from 1 mole % to 40 mole % C₂ to C₅ alkane,based on per mole of feed. The remainder of the feed, if any, cancomprise diluent, for example.

The source of substantially-saturated hydrocarbon (e.g., the firstand/or second substantially-saturated hydrocarbon) is not critical. Apreferred source is natural gas, particularly wet natural gas, that isnatural gas containing some or all of the higher hydrocarbons,particularly C₂ to C₅ hydrocarbon, co-produced with methane. Aparticularly preferred source of natural gas is shale gas. Using thepresent process, the complex and costly process of separating methanefrom the higher hydrocarbons present in natural gas can be obviated andthe natural gas can be converted to easily transportable liquidhydrocarbons by reaction with acetylene. This facility offerssignificant advantages in remote or under-developed locations, where thelack of a pipeline or NGL production infrastructure, may result insignificant quantities of light hydrocarbon (C₁ to C₄) resources beingburned as fuel rather than being recovered. Small scale plants using thepresent process would allow effective recovery of these lighthydrocarbon resources as liquid hydrocarbons.

Any suitable source of acetylene can be used in the present process. Forexample, it is known that acetylene is produced as a by-product in thesteam cracking of hydrocarbons to produce ethylene and from coal by thecalcium carbide process. However, a more preferred source of acetyleneis the partial combustion of methane, for example using the processdisclosed in U.S. Pat. No. 6,365,792, the entire contents of which areincorporated herein by reference. Another preferred source of acetyleneis from the pyrolysis of methane, for example using a reverse flowregenerative reactor system such as is disclosed in U.S. Pat. No.8,119,076, the entire contents of which are incorporated herein byreference.

A preferred source of both the acetylene and methane is an acetylenegeneration process that feeds methane or wet natural gas where only aportion of the methane is converted. An even more preferred process isone in which both the acetylene and methane are effluents from anacetylene generation process that feeds methane or wet natural gas whereonly a portion of the methane is converted and the reactor effluent isclose coupled to a second conversion reactor containing a molecularsieve and a dehydrogenation component.

The present process comprises contacting the above-described feed with acatalyst comprising at least one molecular sieve and at least onedehydrogenation component under conditions effective to convert at leastpart of methane and the acetylene and, where present, the C₂ to C₅alkane to aromatics. Such conditions include exposing the feed in thepresence of the catalyst to a temperature ≧300° C., e.g., in the rangeof 300° C. to 700° C., such as in the range of from 350° C. to 650° C.,or 400° C. to 500° C. Suitable conditions can further include a pressurein the range of from 110 kPa to 450 kPa (absolute). Feed gas hourlyspace velocity can be, e.g., ≧200 cm³/h/g of catalyst, such as in therange of 200 cm³/h/g of catalyst to 20,000 cm³/h/g of catalyst. Certaincatalysts useful in the invention will now be described in more detail.The invention is not limited to these catalysts, and this description isnot meant to foreclose other catalysts within the broader scope of theinvention.

In certain aspects, the catalyst comprises at least one medium pore sizemolecular sieve having a Constraint Index of 2-12 (as defined in U.S.Pat. No. 4,016,218). Examples of such medium pore molecular sievesinclude ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48 andmixtures and intermediates thereof. ZSM-5 is described in detail in U.S.Pat. No. 3,702,886 and Re. 29,948. ZSM-11 is described in detail in U.S.Pat. No. 3,709,979. A ZSM-5/ZSM-11 intermediate structure is describedin U.S. Pat. No. 4,229,424. ZSM-12 is described in U.S. Pat. No.3,832,449. ZSM-22 is described in U.S. Pat. No. 4,556,477. ZSM-23 isdescribed in U.S. Pat. No. 4,076,842. ZSM-35 is described in U.S. Pat.No. 4,016,245. ZSM-48 is more particularly described in U.S. Pat. No.4,234,231.

In other aspects, the catalyst employed in the present process comprisesat least one molecular sieve of the MCM-22 family As used herein, theterm “molecular sieve of the MCM-22 family” (or “material of the MCM-22family” or “MCM-22 family material” or “MCM-22 family zeolite”) includesone or more of:

(i) molecular sieves made from a common first degree crystallinebuilding block unit cell, which unit cell has the MWW frameworktopology. (A unit cell is a spatial arrangement of atoms which if tiledin three-dimensional space describes the crystal structure. Such crystalstructures are discussed in the “Atlas of Zeolite Framework Types”,Fifth edition, 2001, the entire content of which is incorporated asreference);

(ii) molecular sieves made from a common second degree building block,being a 2-dimensional tiling of such MWW framework topology unit cells,forming a monolayer of one unit cell thickness, preferably one c-unitcell thickness;

(iii) molecular sieves made from common second degree building blocks,being layers of one or more than one unit cell thickness, wherein thelayer of more than one unit cell thickness is made from stacking,packing, or binding at least two monolayers of one unit cell thickness.The stacking of such second degree building blocks can be in a regularfashion, an irregular fashion, a random fashion, or any combinationthereof; and

(iv) molecular sieves made by any regular or random 2-dimensional or3-dimensional combination of unit cells having the MWW frameworktopology.

Molecular sieves of the MCM-22 family include those molecular sieveshaving an X-ray diffraction pattern including d-spacing maxima at12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom. The X-raydiffraction data used to characterize the material are obtained bystandard techniques using the K-alpha doublet of copper as incidentradiation and a diffractometer equipped with a scintillation counter andassociated computer as the collection system.

Materials of the MCM-22 family include MCM-22 (described in U.S. Pat.No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409), SSZ-25(described in U.S. Pat. No. 4,826,667), ERB-1 (described in EuropeanPatent No. 0293032), ITQ-1 (described in U.S. Pat. No 6,077,498), ITQ-2(described in International Patent Publication No. WO97/17290), MCM-36(described in U.S. Pat. No. 5,250,277), MCM-49 (described in U.S. Pat.No. 5,236,575), MCM-56 (described in U.S. Pat. No. 5,362,697), andmixtures thereof. Related zeolite UZM-8 is also suitable for use as amolecular sieve component of the present catalyst.

In certain aspects, the molecular sieve employed in the present processmay be an aluminosilicate or a substituted aluminosilicate in which partof all of the aluminum is replaced by a different trivalent metal, suchas gallium or indium.

The invention can be practiced using catalysts that have been subjectedto one or more catalyst treatments, e.g., selectivation. For example,the catalyst can comprises at least one molecular sieve which has beenselectivated, either before introduction of the catalyst into thereactor or in-situ in the reactor, by contacting the catalyst with aselectivating agent, such as at least one organosilicon in a liquidcarrier and subsequently calcining the catalyst at a temperature of 350to 550° C. This selectivation procedure can be repeated two or moretimes and alters the diffusion characteristics of the catalyst such thatthe formation of para-xylene over other xylene isomers is favored. Sucha selectivation process is described in detail in U.S. Pat. Nos.5,633,417 and 5,675,047, the entire contents of which are incorporatedherein by reference.

In addition to the molecular sieve component, the catalyst generallycomprises at least one dehydrogenation component, e.g., at least onedehydrogenation metal. The dehydrogenation component is typicallypresent in an amount of at least 0.1 wt. %, such as from 0.1 to 5 wt. %,of the overall catalyst. The dehydrogenation component can comprise oneor more neutral metals selected from Groups 3 to 13 of the PeriodicTable of the Elements, such as Ga, In, Zn, Cu, Re, Mo, W, La, Fe, Ag,Pt, Pd, and/or one or more oxides, sulfides and/or carbides of thesemetals. The dehydrogenation component can be provided on the catalyst inany manner, for example by conventional methods such as impregnation orion exchange of the molecular sieve with a solution of a compound of therelevant metal, followed by conversion of the metal compound to thedesired form, namely neutral metal, oxide, sulfide and/or carbide. Partor all of the dehydrogenation metal may also be present in thecrystalline framework of the molecular sieve.

In one preferred embodiment, the bifunctional catalyst used in thepresent process is selected from the group consisting of Ga and/orIn-modified ZSM-5 type zeolites such as Ga and/or In-impregnatedH-ZSM-5, Ga and/or In-exchanged H-ZSM-5, H-gallosilicate of ZSM-5 typestructure and H-galloaluminosilicate of ZSM-5 type structure. Thesezeolites can also be prepared by any suitable method, includingconventional methods.

For example, the bifunctional catalyst may contain tetrahedral aluminiumand/or gallium, which is present in the zeolite framework or lattice,and octahedral gallium or indium, which is not present in the zeoliteframework but present in the zeolite channels in close vicinity to thezeolitic protonic acid sites, and which is attributed to the presence oftetrahedral aluminum and gallium in the catalyst. The tetrahedral orframework Al and/or, Ga is responsible for the acid function of thecatalyst and octahedral or non-framework Ga and/or In is responsible forthe dehydrogenation function of the catalyst. In one preferredembodiment, the bifunctional catalyst comprises H-galloaluminosilicateof ZSM-5 type structure having framework (tetrahedral) Si/Al and Si/Gamole ratios of about 10:1 to 100:1 and 15:1 to 150:1, respectively, andnon-framework (octahedral) Ga of about 0.5 to 0 wt. %.

In addition to the molecular sieve components and dehydrogenationcomponent, the catalyst may be composited with another material which isresistant to the temperatures and other conditions employed in theconversion reaction. Such materials include active and inactivematerials and synthetic or naturally occurring zeolites as well asinorganic materials such as clays and/or oxides such as alumina, silica,silica-alumina, zirconia, titania, magnesia or mixtures of these andother oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Clays may also be included with the oxide type binders tomodify the mechanical properties of the catalyst or to assist in itsmanufacture. Use of a material in conjunction with the molecular sieve,i.e., combined therewith or present during its synthesis, which itselfis catalytically active may change the conversion and/or selectivity ofthe catalyst. Inactive materials suitably serve as diluents to controlthe amount of conversion so that products may be obtained economicallyand orderly without employing other means for controlling the rate ofreaction. These materials may be incorporated into naturally occurringclays, e.g., bentonite and kaolin, to improve the crush strength of thecatalyst under commercial operating conditions and function as bindersor matrices for the catalyst. The relative proportions of molecularsieve and inorganic oxide matrix vary widely, with the sieve contentranging from about 1 to about 90 percent by weight and more usually,when the composite is prepared in the form of beads, in the range ofabout 2 to about 80 weight percent of the composite.

Conversion of a feed comprising methane and acetylene to aromatics isgenerally conducted at a temperature of at least 300° C., e.g., atemperature in the range of about 300° C. to 650° C., such as 300° C. to500° C., or 300° C. to 400° C., or 300° C. to 390° C., or 300° C. to375° C., or 300° C. to 350° C. In particular aspects the conversion iscarried out at a temperature in the range of from 350° C. to 650° C.,e.g., from 350° C. to 390° C., or 350° C. to 375° C. The pressure duringthe conversion is typically in the range of from 110 kPa to 450 kPa(absolute). Where the feed comprises methane, acetylene and alsocontains C₂ to C₅ alkane, the aromatics yield is increased even at lowertemperatures in this range, particularly in the range of from 300° C. to500° C., and more particularly in the range of 300° C. to 400° C., andeven more particularly in the range of 300° C. to 390° C., or 300° C. to375° C., or 325° C. to 375° C., or 350° C. to 375° C. The conversionprocess can be conducted in one or more fixed bed, moving bed orfluidized bed reaction zones. The conversion can be operated, e.g.,continuously, semi-continuously, or in batch mode.

The products of the conversion are mainly C₆ to C₁₀ aromatics andmolecular hydrogen, with smaller amounts of ethylene, ethane, propylene,propane, C₄ hydrocarbons and traces of C₅₊ aliphatic hydrocarbons (e.g.,oligomers). The aromatic product slate tends to be rich in toluene andxylenes, whereas aromatization of acetylene alone favors the productionof benzene. The C₆ to C₁₀ aromatics generally comprise at least 5 wt. %of the product, based on the weight of the product, e.g. ≧10 wt. %, suchas ≧15 wt. %. Aromatics can readily be removed from the other conversionproducts and any residual methane and co-reactants by any convenientmethod, e.g., well known fractionation and extraction techniques.

Where it is desired to maximize the production of xylenes, it may beadvantageous to include an oxygenate, such as syngas and/or alcohol,typically methanol, in the methane containing feed so that most of thebenzene and toluene is produced as an intermediate and is then furtheralkylated via the oxygenate to xylenes. By employing a selectivatedcatalyst as described above, the relative yield of para-xylene can beincreased.

In certain aspects, an Oxidative Coupling of Methane (OCM) is utilizedin conjunction with the specified aromatization process. OCM is aprocess in which methane is reacted with an oxygen-containing gas in thepresence of a catalyst, such as an alkaline earth/rare earth metal oxidecatalyst, such as Sr-promoted La₂O₃, at a temperature of 600 to 800° C.and a pressure is 1 to 10 bar. The reaction is described in, forexample, U.S. Pat. No 5,336,825, the entire contents of which areincorporated herein by reference. The process couples the methane intoto higher hydrocarbons, such as ethylene, by reactions such as:2CH₄+O₂→C₂H₄+2H₂Owith a typical C₂ yield of 26 to 29% and with about ⅔ of the C₂hydrocarbons being ethylene. The overall product composition from theOCM reaction is 70 mole % to 95 mole % unconverted methane, 5 mole % to30 mole % olefin, 1 mole % to 5 mole % CO2, and 1 mole % to 5 mole %H₂O, the mole percents being per mole of product. Combining OCM with thespecified aromatization process, e.g., by operating OCM upstream of thearomatization process, is believed to be beneficial because the olefinscan be utilized as a co-reactant with the acetylene to increase theefficiency of the aromatization process over aromatization efficiencyusing methane and acetylene only.

In certain aspects, the feed to the specified aromatization comprisesacetylene and at least a portion of product obtained from OCM, e.g., bydiverting away at least a portion of the OCM product toward thearomatization process. For example, the feed's firstsubstantially-saturated hydrocarbon can comprise ≧99.0 wt. % ofunconverted methane obtained from OCM, based on the weight of the firstsubstantially-saturated hydrocarbon. Optionally, the feed to thearomatization process comprises acetylene, ≧70 vol. % unconvertedmethane obtained from OCM, and ≧5 vol. % of olefin, the volume percentsbeing per volume of feed to the aromatization. The balance of the feed,if any, can be diluent, e.g., diluent obtained from OCM product, such as≧1 vol. % of CO₂ and/or ≧1 volume % of H2O. Generally the molar ratio ofunconverted OCM methane to acetylene in the feed is in the range of from0.6:1 to 20:1, such as from 4:1 to 10:1, for example from 5:1 to 10:1.Generally the molar ratio of olefin to acetylene in the feed is in therange of from 0.1:1 to 20:1 such as from 2:1 to 10:1, for example from3:1 to 10:1. Examples of suitable feeds comprise from 70 mole % to 95mole % of unconverted OCM methane and 5 mole % to 30 mole % of olefin,based on per mole of feed. The remainder of the feed, if any, cancomprise diluent, for example

In certain aspects, the total effluent from the OCM reaction zone can beconducted to the aromatization step, e.g., without any interveningseparations and preferably without any need for heat exchange (the OCMreaction is exothermic). The second conversion step (the aromatization)can be operated under substantially the same conditions and can utilizesubstantially the same catalyst, as specified for aromatizing acetyleneand the first substantially-saturated hydrocarbon (optionally incombination with the second substantially-saturated hydrocarbon and/ordiluent).

In certain aspects, the second step includes oligomerization (instead ofor in addition to aromatization), wherein the effluent, from theoligomerization reaction comprises ≧5 wt. % of C₅₊ hydrocarbons, basedon the weight of the effluent, such as C₅₊ oligomers of order ≧2. Inthese aspects, the oligomerization reaction can be exothermic, andmethane can be incorporated into the oligomerization reaction. In otheraspects, the two steps may be combined into one, with catalyticfunctionalities for OCM and aromatization or OCM and oligomerizationbeing combined into one catalyst bed and the process being carried outin a single reaction zone.

All patents, test procedures, and other documents cited herein,including priority documents, are fully incorporated by reference to theextent such disclosure is not inconsistent and for all jurisdictions inwhich such incorporation is permitted.

While the illustrative forms disclosed herein have been described withparticularity, it will be understood that various other modificationswill be apparent to and can be readily made by those skilled in the artwithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the scope of the claims appendedhereto be limited to the examples and descriptions set forth herein butrather that the claims be construed as encompassing all the features ofpatentable novelty which reside herein, including all features whichwould be treated as equivalents thereof by those skilled in the art towhich this disclosure pertains.

When numerical lower limits and numerical upper limits are listedherein, ranges from any lower limit to any upper limit are contemplated,and are expressly within the scope of the invention. The term“comprising” is synonymous with the term “including”. Likewise whenevera composition, an element or a group of components is preceded with thetransitional phrase “comprising”, it is understood that we alsocontemplate the same composition or group of components withtransitional phrases “consisting essentially of,” “consisting of”,“selected from the group of consisting of,” or “is” preceding therecitation of the composition, component, or components, and vice versa.

The invention claimed is:
 1. A process for producing C₅₊ hydrocarbon,the process comprising: (a) contacting a feed comprising methane with anoxygen-containing gas in the presence of a first catalyst underconditions effective to oxidatively couple the methane to produce aneffluent containing C₂₊ hydrocarbons and unconverted methane; (b)combining acetylene and at least a portion of the effluent from (a) toproduce a second feed, wherein (i) the second feed contains theunconverted methane in an amount of at least 9 mole % based on per moleof the feed, (ii) the second feed contains at least a portion of the C₂₊hydrocarbon in the effluent, and (iii) the second feed has a molar ratioof the unconverted methane to the acetylene in the range of from 0.6:1to 20:1; (c) contacting the second feed with a second catalystcomprising at least one molecular sieve and at least one dehydrogenationcomponent comprising Ga and/or In under conditions, including atemperature in the range of from 300° C. to 390° C. effective to convertat least a portion of the unconverted methane in the second feed, atleast a portion of the acetylene in the second feed, and at least aportion of the C₂₊ hydrocarbon in the second feed to a productcomprising at least 5 wt. % of aromatics, based the weight of theproduct; and (d) separating at least part of the aromatics from theproduct.
 2. The process of claim 1, wherein the feed further comprisesone or more C₂ to C₅ alkane.
 3. The process of claim 2, wherein at leastpart of the methane and C₂ to C₅ alkane in the feed is derived fromnatural gas.
 4. The process of claim 1, wherein the first and secondcatalysts are contained in the same reaction zone.